The designated competent person should have and be able to demonstrate the following

Ability to detect- conditions that could result in cave-ins- failures in protective systems- hazardous atmospheres and- other hazards including those associated with confined spaces.

19Competent Person

The designated competent person should have

Authority to take prompt corrective measures to eliminate existing and predictable hazards and to stop work when required.

20Excavation

An Excavation is any man-made cut, cavity, trench, or depression in an earth surface that is formed by earth removal.

21Ingress Egress

Ingress And Egress mean "entry" and "exit," respectively. In trenching and excavation operations, they refer to the provision of safe means for employees to enter or exit an excavation or trench.

22Ingress Egress

Access to and exit from the trench require the following conditions

Trenches 4 feet or more in depth should be provided with a fixed means of egress.

Spacing between ladders or other means of egress must be such that a worker will not have to travel more than 25 feet laterally to the nearest means of egress.

Ladders must be secured and extend a minimum of 36 inches above the landing.

Metal ladders should be used with caution, particularly when electric utilities are present.

23Hazardous Atmosphere

Hazardous Atmosphere is an atmosphere that by reason of being explosive, flammable, poisonous, corrosive, oxidizing, irritating, oxygen-deficient, toxic, or otherwise harmful may cause death, illness, or injury to persons exposed to it.

24Trench

A Trench is a narrow excavation (in relation to its length).

In general, the depth of a trench is greater than its width, and the width (measured at the bottom) is not greater than 15 ft.

If a form or other structure installed or constructed in an excavation reduces the distance between the form and the side of the excavation to 15 ft or less (measured at the bottom of the excavation), the excavation is also considered to be a trench.

25Protective System

Protective System refers to a method of protecting employees from cave-ins, from material that could fall or roll from an excavation face or into an excavation, and from the collapse of adjacent structures.

Protective systems include support systems, sloping and benching systems, shield systems, and other systems that provide the necessary protection.

Surface crossing should be discouraged. If needed, vehicle crossings must be designed by and installed under the supervision of a registered professional engineer.

Walkways or bridges must be provided for foot traffic. These structures shall

have a safety factor of 4

have a minimum clear width of 20 inches

be fitted with standard rails and

extend a minimum of 24 inches past the surface edge of the trench.

29Exposure to Falling Loads

Employees must be protected from loads or objects falling from lifting or digging equipment. Procedures include

Employees are not permitted to work under raised loads.

Employees are required to stand away from equipment that is being loaded or unloaded.

Equipment operators or truck drivers may stay in their equipment during loading and unloading if the equipment is properly equipped with a cab shield or adequate canopy.

30Exposure to Vehicles

Procedures to protect employees from being injured or killed by vehicle traffic include

Providing employees with and requiring them to wear warning vests or other suitable garments marked with or made of reflective or high-visibility materials.

Requiring a designated, trained flag-person along with signs, signals, and barricades when necessary.

31Mobile Systems Warning

The following steps should be taken to prevent vehicles from accidentally falling into the trench

Barricades must be installed where necessary.

Hand or mechanical signals must be used as required.

Stop logs must be installed if there is a danger of vehicles falling into the trench.

Soil should be graded away from the excavation this will assist in vehicle control and channeling of run-off water.

32Hazardous Atmospheres Confined Spaces (1)

Employees shall not be permitted to work in hazardous and/or toxic atmospheres. Such atmospheres include those with

Less than 19.5 or more than 23.5 oxygen

A combustible gas concentration greater than 20 of the lower flammable limit and

Concentrations of hazardous substances that exceed those specified in the Threshold Limit Values for Airborne Contaminants established by the ACGIH (American Conference of Governmental Industrial Hygienists).

Type C soils include granular soils such as gravel, sand and loamy sand, submerged soil, soil from which water is freely seeping, and submerged rock that is not stable.

65Type C Soil

Also included in this classification is material in a sloped, layered system where the layers dip into the excavation or have a slope of four horizontal to one vertical (4H1V) or greater.

66Soil Classification 67Soil Classification

The visual and manual analyses, such as those noted as being acceptable in the regulations, shall be designed and conducted to provide sufficient quantitative and qualitative information as may be necessary to identify properly the properties, factors, and conditions affecting the classification of the deposits.

68Soil Classification

Each soil and rock deposit shall be classified by a competent person as Stable Rock, Type A, Type B, or Type C.

The classification of the deposits shall be made based on the results of at least one visual and at least one manual analysis.

69Layered Systems

Layered systems. In a layered system, the system shall be classified in accordance with its weakest layer.

Each layer may be classified individually where a more stable layer lies under a less stable layer.

70Reclassification of Soil

If, after classifying a deposit, the properties, factors, or conditions affecting its classification change in any way, the changes shall be evaluated by a competent person.

The deposit shall be reclassified as necessary to reflect the changed circumstances

71Visual Evaluation 72Visual Evaluation

A visual test is a qualitative evaluation of conditions around the site.

The entire excavation site is observed, including the soil adjacent to the site and the soil being excavated.

If the soil remains in clumps, it is cohesive if it appears to be coarse-grained sand or gravel that does not clump, it is considered granular.

The evaluator also checks for any signs of vibration.

73Visual Evaluation

During a visual test, the evaluator should check for

crack-line openings along the failure zone that would indicate tension cracks,

look for existing utilities or or other underground structures that indicate that the soil has previously been disturbed, and

observe the open side of the excavation for indications of layers and the slope of those layers.

74Visual Evaluation

The evaluator should also look for signs of bulging, boiling, or sloughing (spalling), as well as for signs of surface water seeping from the sides of the excavation or from the water table.

If there is standing water in the cut, the evaluator should check for "quick" conditions.

75Visual Evaluation

The evaluator should check for surcharging and the spoil distance from the edge of the excavation.

Sources of vibration should also be noted that may affect the stability of the excavation face.

76Manual Evaluation 77Soil Test Equipment

Pocket Penetrometers are direct-reading, spring-operated instruments used to determine the unconfined compressive strength of saturated cohesive soils. Once pushed into the soil, an indicator sleeve displays the reading. The instrument is calibrated in either tons per square foot (tsf) or kilograms per square centimeter (kPa).

Penetrometers have error rates in the range of 20-40.

78Soil Test Equipment

Shearvane (Torvane). To determine the unconfined compressive strength of the soil with a shearvane, the blades of the vane are pressed into a level section of undisturbed soil, and the torsion knob is slowly turned until soil failure occurs. The direct instrument reading must be multiplied by 2 to provide results in tons per square foot (tsf) or kilograms per square centimeter (kPa).

79Thumb Penetration Soil Test

The thumb penetration procedure involves an attempt to press the thumb firmly into the soil in question.

If the thumb makes an indentation in the soil only with great difficulty, the soil is probably Type A.

80Thumb Penetration Soil Test

If the thumb penetrates no further than the length of the thumb nail, it is probably Type B soil.

81Thumb Penetration Soil Test

If the thumb penetrates the full length of the thumb, it is Type C soil.

The thumb test is subjective and is therefore the least accurate of the three methods.

82Dry Strength Soil Test

Dry soil that crumbles freely or with moderate pressure into individual grains is granular.

Dry soil that falls into clumps that subsequently break into smaller clumps (and the smaller clumps can be broken only with difficulty) is probably clay in combination with gravel, sand, or silt.

83Dry Strength Soil Test

If the soil breaks into clumps that do not break into smaller clumps (and the soil can be broken only with difficulty), the soil is considered unfissured, unless there is visual indication of fissuring.

84Wet Thread Soil Test

This test is conducted by molding a moist sample of the soil into a ball and attempting to roll it into a thin thread approximately 1/8 inch in diameter (thick) by 2 inches in length.

The soil sample is held by one end. If the sample does not break or tear, the soil is considered cohesive.

85Drying Test

Dry a sample that is approximately 1 inch thick by 6 inches in diameter until thoroughly dry. If it cracks as it dries, significant fissures are possible.

86Drying Test

Samples that dry without cracking are broken by hand.

If it breaks with difficulty, it is unfissured cohesive material.

It it breaks easily by hand, it is either fissured cohesive material or granular.

87Drying Test

To distinguish between the two, pulverize the dried clumps by hand or by stepping on them.

If the clumps do not pulverize easily, the material is cohesive with fissures.

If the clumps pulverize into very small fragments the material is granular.

88Protective Systems 89Protective Systems

Shoring

Shielding

Sloping

Benching

90Shoring

Shoring is the provision of a support system for trench faces used to prevent movement of soil, underground utilities, roadways, and foundations.

91Shoring

Shoring (or shielding) is used when the location or depth of the cut makes sloping back to the maximum allowable slope impractical.

92Shoring Types

Shoring systems consist of posts, wales, struts, and sheeting. Three basic types of shoring are

Timber

Hydraulic

Pneumatic

93Timber Shoring 94Hydraulic Shoring

The trend today is toward the use of hydraulic shoring, a prefabricated strut and/or wale system manufactured of aluminum or steel.

Hydraulic shoring provides a critical safety advantage over timber shoring because workers do not have to enter the trench to install or remove hydraulic shoring.

95Hydraulic Shoring

Other advantages of most hydraulic systems are that they

Are light enough to be installed by one worker

Are gauge-regulated to ensure even distribution of pressure along the trench line

Can have their trench faces "preloaded" to use the soil's natural cohesion to prevent movement and

Can be adapted easily to various trench depths and widths.

96Hydraulic Shoring

All shoring should be installed from the top down and removed from the bottom up.

Hydraulic shoring should be checked at least once per shift for leaking hoses and/or cylinders, broken connections, cracked nipples, bent bases, and any other damaged or defective parts.

Trench boxes are generally used in open areas, but they also may be used in combination with sloping and benching.

The box should extend at least 18 inches above the surrounding area if there is sloping toward excavation.

This can be accomplished by providing a benched area adjacent to the box.

136Slope Shield

Earth excavation to a depth of 2 feet below the shield is permitted, but only if the shield is designed to resist the forces calculated for the full depth of the trench and there are no indications while the trench is open of possible loss of soil from behind or below the bottom of the support system.

137Slope Shield

Conditions of this type require observation on the effects of bulging, heaving, and boiling as well as surcharging, vibration, adjacent structures, etc., on excavating below the bottom of a shield.

Careful visual inspection of the conditions mentioned above is the primary and most prudent approach to hazard identification and control.

138Slope Shield 139Slope and Shield 140Slope and Shield 141Benching

There are two basic types of benching, simple and multiple.

The type of soil determines the horizontal to vertical ratio of the benched side.

142Benching

As a general rule, the bottom vertical height of the trench must not exceed 4 feet for the first bench.

Subsequent benches may be up to a maximum of 5 feet vertical in Type A soil and 4 feet in Type B soil to a total trench depth of 20 feet.

143Benching

All subsequent benches must be below the maximum allowable slope for that soil type.

For Type B soil the trench excavation is permitted in cohesive soil only.

144B Soil Single Bench 145B Soil Multiple Bench 146Slope and Bench

Maximum allowable slopes for excavations less than 20 feet based on soil type and angle to the horizontal are as follows

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